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Glossary

Aberration - A term from optics that refers to anything affecting the fidelity of the image in regards to the original scene.

 

AC - Alternating current.

 

Activity detection - Refers to a method built into some multiplexers for detecting movement within the camera’s field of view (connected to the multiplexer), which is then used to improve camera recording update rate.

 

AC/DC - Alternating current and direct current.

 

A/D (AD) - Usually refers to analog to digital conversion.

 

ADC - Analog to digital conversion.    This is usually the very first stage of an electronic device that processes signals into digital format.    The signal can be video, audio, control output and similar.

 

AGC - Automatic gain control.    A section in an electronic circuit that has feedback and regulates a certain voltage level to fall within predetermined margins.

 

ALC - Automatic light control.    A part of the electronics of an automatic iris lens that has a function similar to backlight compensation in photography.

 

Aliasing. - An occurrence of sampled data interference.    This can occur in CCD image projection of high spatial frequencies and is also known as Moiré patterning.    It can be minimized by a technique known as optical low pass filtering.

 

Alphanumeric   video generator   (also text inserter)     -  A device for providing   additional information, normally superimposed on the picture being displayed; this can range from one or two characters to full-screen alphanumeric text.   Such generators use the incoming video signal sync pulses as a reference point for the text insertion position, which means if the video signal is of poor quality, the text stability will also be of poor quality.

 

Amplitude - The maximum value of a varying waveform.

 

Analog signal - Representation of data by continuously varying quantities.    An analog electrical signal  has  a  different  value  of  volts  or  amperes  for  electrical  representation  of  the  original excitement (sound, light) within the dynamic range of the system.

 

ANSI - American National Standards Institute.

 

Anti-aliasing  - A procedure  employed  to  eliminate  or reduce  (by  smoothing  and  filtering)  the aliasing effects.

 

Aperture  - The opening of a lens that controls the amount of light reaching the surface of the pickup device.    The size of the aperture is controlled by the iris adjustment.    By increasing the F-stop number (F/1.4, F/1.8, F/2.8, etc.) less light is permitted to pass to the pickup device.

 

Apostilb  - A photometric unit for measuring  luminance  where, instead of candelas,  lumens are used to measure the luminous flux of a source.

 

 

Archive  - Long-term  off-line  storage.    In digital  systems,  pictures  are  generally  archived  onto some form of hard disc, magnetic tape, floppy disk or DAT cartridge.

 

Artifacts - Undesirable elements or defects in a video picture.    These may occur naturally in the video  process  and  must  be  eliminated  in  order  to  achieve  a  high-quality  picture.    The  most common are cross-color and cross-luminance.

 

ASCII - American Standard Code for Information Interchange.    A 128-character  set that includes the upper case and lower-case English alphabet, numerals, special symbols and 32 control codes. A 7-bit binary number represents  each character.    Therefore, one ASCII-encoded  character can be stored in one byte of computer memory.

 

Aspect  ratio - This is the ratio between  the width and height of a television  or cinema  picture display.    The present aspect ratio of the television screen is 4:3, which means four units wide by three units high.   Such aspect ratio was elected in the early days of television, when the majority of movies were of the same format.    The new, high definition television format proposes a 16:9 aspect ratio.

 

Aspherical  lens - A lens that has an aspherical  surface.    It is harder  and more expensive  to manufacture, but it offers certain advantages over a normal spherical lens.

 

Astigmatism - The uneven foreground and background blur that is in an image.

 

Asynchronous  - Lacking  synchronization.    In video,  a signal  is asynchronous  when  its timing differs from that of the system reference signal.    A foreign video signal is asynchronous before a local frame synchronizer treats it.

 

ATM - Asynchronous  transfer mode.    A transporting  and switching method in which information does not occur periodically with respect to some reference such as a frame pattern.

Attenuator  -  A circuit  that  provides  reduction  of  the  amplitude  of  an  electrical  signal  without introducing appreciable phase or frequency distortion.

 

ATSC - Advanced Television System Committee  (think of it as a modern NTSC).    An American committee involved in creating the high definition television standards.

 

Attenuation - The decrease in magnitude of a wave, or a signal, as it travels through a medium or an electric system.    It is measured in decibels (dB).

 

Auto iris (AI) - An automatic method of varying the size of a lens aperture in response to changes in scene illumination.

 

AWG - American wire gauge.    A wire diameter specification based on the American standard.

The smaller the AWG number, the larger the wire diameter (see the reference table in the Camera

Power Supply section).

 

 

 

 

*This glossary contains a list of general terms and definitions related to surveillance systems, security cameras, and CCTV equipment and much more.

*Saw-C-look provides iinformation for informational purposes only. We reserve the right to alter it at any time, and do not guarantee its accuracy, or completeness.

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